The present invention relates to a compressor with a variable piston stroke or displacement volume, particularly an air-conditioning compressor for a motor vehicle, with a piston-drive mechanism in which a revolving wobble plate is driven by a driving shaft that is rotatably supported by parts of the compressor housing. The height of the piston stroke is variable and can be regulated by a flow of pressure medium from the high-pressure outlet compartment of the compressor to the driving compartment (i.e., the compartment that contains the wobble plate, also referred to herein as piston-drive compartment), and/or by a flow of pressure medium from the driving compartment to the intake suction compartment. An end portion of the driving shaft extends from the driving compartment into a housing part such as the cylinder head of the compressor. The inflow of pressure medium into the driving compartment can be realized at the outside surface of the end portion of the shaft, while the outflow of pressure medium from the driving compartment can be realized through a hollow space in the end portion of the shaft. Compressors with a variable piston stroke according to the foregoing description belong to the known state of the art. In these compressors, the end portion of the shaft that extends into the cylinder head can be used as a conduit and also as a separating wall between the streams of pressure medium flowing into and out of the driving compartment. For example, the inflow of pressure medium into the driving compartment may be routed along the outside wall of the end portion of the driving shaft. The outflow of pressure medium from the driving compartment to the low-pressure zone of the compressor can be routed through a hollow bore channel in the driving shaft. An important factor in this arrangement is the ability to seal the in-flowing pressure medium against the out-flowing pressure medium in the area of the end portion of the driving shaft. In the known state-of-the-art compressors, this sealing function is performed by a shaft seal ring that is inserted between the end portion of the driving shaft and the wall of the recess that receives the end portion of the driving shaft, e.g. in the cylinder head. The additional cost of the shaft seal rings and their installation represents a drawback of the state-of-the-art compressors of the foregoing description.
The present invention therefore has the objective to propose a compressor which, by virtue of its design concept, is free of the aforementioned disadvantages.
The invention offers a solution that meets the foregoing objective for a compressor with a variable piston stroke or displacement volume, particularly an air-conditioning compressor for a motor vehicle, with a piston-drive mechanism in which a revolving wobble plate is driven by a driving shaft that is rotatably supported by parts of the compressor housing. The variable height of the piston stroke can be regulated by a flow of pressure medium from the high-pressure outlet compartment of the compressor to the driving compartment, and/or by a flow of pressure medium from the driving compartment to the intake suction compartment. An end portion of the driving shaft extends from the driving compartment into a housing part such as the cylinder head of the compressor. The inflow of pressure medium into the driving compartment can be realized at the outside surface of the end portion of the shaft, while the outflow of pressure medium from the driving compartment can be realized through a hollow space in the end portion of the shaft. In the area where the pressure medium enters the flow path from the high-pressure zone to the driving compartment, the compressor according to the invention has a flow-resisting element or feature between the end portion of the driving shaft and the wall of the recess that receives the end portion of the driving shaft, e.g., in the cylinder head, so that the resistance to the flow of fluid is significantly greater in the direction towards the end of the shaft and into the cylinder head than the flow resistance of the conduits leading along the outside surface of the end portion of the shaft in the direction towards the driving compartment. According to a preferred concept of the inventive compressor, the stronger resistance to a fluid flow in the direction towards the end of the driving shaft is realized through a ring-shaped narrow gap between the end portion of the driving shaft and the wall of the recess that receives the end portion of the driving shaft.
In a preferred embodiment of the inventive compressor, the end portion of the driving shaft is represented by a tubular extension that is seated on the shaft.
A further embodiment of the compressor according to the invention is distinguished by a conveyor helix or screw thread which generates a propellant effect in the direction towards the driving compartment when the driving shaft is rotating. In another embodiment of the compressor according to the invention, the end portion of the driving shaft has a profile resembling a helical gear tooth profile, which likewise generates a propellant effect in the direction towards the driving compartment when the driving shaft is rotating.
In a further preferred embodiment of the invention, the end portion of the driving shaft has a conical shape that widens towards the end, so that the gap becomes narrower towards the end of the driving shaft.
Also preferred is an embodiment of the compressor where the gap works as a lubricant barrier or oil barrier. In yet another embodiment according to the invention, the lubricant film in the gap is used as a fluid seal against the gaseous pressure medium. Further preferred is an embodiment where the gap has a width of approximately 0.5 mm.